Light sensitive cell



Dec. 19, 1933. A, w. CARPENTER 1,940,245

LIGHT SENSITIVE CELL .Filed sept. 3. 1930' INVENTOR Arf/,wf M4 Car/ocx "r ATTORNEY Patented Dec. 19, 1933 UNITED STATES PATENT OFFICE? to United Research Co rporation, New York,

N. Y., a corporation. Delaware Application September 3, 1930. Serial No. 479,511

s claim. (ci. zul-s3) This invention relates to light sensitive cells, and particularly to conductive coatings and support members for cells utilizing substances which change their electrical characteristics in the presence of light.

In the production of light sensitive cells, it is desirable that the cells be made by such processes and include such construction details as will permit of building them with a minimum loss from defective parts. It is also desirable that the cells produced have a high sensitivity and a high response to light, and also that the incidental noises in th cell caused by the normal current therein, which are commonly known as-ground tone", be as low as possible, in order to obtain a high ratio between the ground tone intensity and the response intensity.

An object of the invention is to reduce the ground noise in a light sensitive cell.

Another object is to increase the lsensitivity of a light sensitive cell.

Still another object is to obtain in a new light sensitive cell firmer adherence of a new conductive material to an insulating base, and to reduce the tendency toward distortion of the base by tension due to heat treatment during processing. h1 the manufacture of light sensitive cells it has been customary to utilize a plate of glass, to which is attached a coating of metal. In this coating a sinuous line of separation is formed to produce a pair of electrodes having interdigitated projections, across which a bridge of photo-sensitive material is placed. In the production of such cells it has been customary to utilize for the conductive metal a thin layer of platinum. It is found, however, that when a substantial thickness of platinum is applied to a thin glass plate, the contraction of the metal produced by the ring operation tends to distort the glass, to an extent which may result in fracture of the glass or pulling away of the metal, thereby reducing or destroying the usefulness of the cell.

It is also well known that many metals form selenides, which are in general analogous to the readily formed on gold than on metals of the platinum-palladium group. This group in.- ciudes those elements of the eighth group of the periodic table embraced by the second to the fourth long period. y

The above objects are accomplished by putting a photo-sensitive substance in contact with a conductive support comprising a mixture of metals.

' The objects of reducing the ground noise intensity and increasing the sensitivity are accomplished by the use, in combination, of a photosensitive substance and a conductive material comprising palladium.

The invention also comprises the utilization of mixtures of resistant metals in the conductive coating in a photo-cell. and particularly of metal such as palladium and the related metals. in combination with .other resistant metals, such as platinum, iridium and osmium. It is further found that other advantageous results may be obtained by the use of still more complex metal mixtures, such as mixtures of platinum, osmium and iridium, either with or without palladium, or metals of the group containing palladium.

'It is thus found that` the introduction into the conductive coating of other resistive metails is advantageous in improving the cell performance.

Similarly. the introduction of other metals into the coating reduces the tendency of the metal to shrink during the firing operation, reducing the danger of breakage of the glass plate, and the `chance of `the metal pulling away from the surface. Thisreduces the loss from defective cells and parts, and accordingly the commercial cost. l

Bythe invention there is thus produced a new and useful light sensitive cell. which is easier to construct and which has a substantially improved performance, a reduced ground noise characteristic, and a substantially increased sensitivity.

Other objects and details of the invention will be apparent from the following description when read in connection with the accompanying drawing wherein:

The single figure isa diagrammatic representation of the device of the invention.

Referring to the drawing, an insulating support 1- is provided, which may preferably be a thin sheet of glass of appropriate size, upon which is applied a conducting coating 2, which is formed in two appropriate separated electrodes, by a dividing space, which may be a sinuous trace producing interdigitated projections. Upon the metallic coating is applied in any appropriate manner a photo-sensitive material 3, which may desirably be selenium in suitable crystalline form.

The metal coating 2 is preferably produced by applying the metals in dispersed form in a suitable vehicle. This may be a colloidal suspension of the metals in a material such as oil of lavender, oil of cloves, or other oil or varnish vehicle. After appropriate application, the grid is then red to volatilize out the vehicle, and leave behind the metal in an adherent coating on the glass.

A mixture of colloidal platinum and colloidal palladium in the proportion of approximately equal parts of each, carried in an oily vehicle is found particularly desirable. The prepared colloidal material may be applied in any `suit lable way upon the desired glassl surface, and fired to produce the desired conductive coating, upon which the selenium may be deposited.

Alternatively the proportion of palladium may be reduced by mixing with the palladium-platinum preparation various proportions of pure colloidal platinum suspended in a similar oily vehicle. In this way the proportion of palladium may be reduced by any desired amount, resulting in the production of cells having different characteristics.

Similarly desirable results may also be obtained by the use of materials containing still higher proportions of palladium, to the extent of using pure palladium. It appears that the very high melting^point and high chemical resistivity are of value in the production of cells upon a coating having a high proportion of palladium. It is reported that a peculiar reaction occurs between palladium and iodine, and in view of the fact that cells are often treated with iodine as disclosed in Patent No. 1,730,- 505, it may be that a favorable palladium-iodine reaction occurs to reduce the noise level and increase the sensitivity.

Certain other valuable effects are obtained by the use of still other of the resistant metals in a cell coating. For this purpose colloidal suspensions may be prepared of other metals such as ruthenium, rhodium, iridium, and osmium, which may conveniently be produced by forming an arc between electrodes of the desired metal under water or oil in the well known manner. These suspensions may then be incorporated in the desired vehicle, and applied in the well known manner, either in pure form or in the desired mixtures. i

Changes of the metal mixture in this manner produce a variety of different operating characteristics, which are still further influenced by the after treatment of the cell. Different results a're obtained with the diiferent metal mixtures, depending upon the character of iodine compound which is applied, and depending upon the temperature at which the photo-sensitive material is applied, the character of the photo-sensitive substance, whether of pure selenium. mixtures of selenium and other substances, or other of the compounds which show sensitivity to light. In this way a desirable after treatment may be-chosen for the production of desired characteristics in the cells, and the base metal may be correspondingly chosen accordingto the desired characteristic of the cell, to accentuate phenomena obtained by the choice of processing.

Likewise, the incorporation of any of the mentioned'metals favorably inuences the tendency toward shrinkage during the firing operation.

By the invention as above described, a new and previously unused metal is thus utilized for a light sensitive cell whereby there are obtained the new and useful features of better performance, lower ground noise, and higher sensitivity.

While there are disclosed but a limited number of embodiments of the invention in the above description, it is possible to produce still other modifications thereof without departing from the inventive concept therein disclosed, and it is accordingly desired that only such limitations shall be imposed upon the appended claims as are stated'therein, or required by the prior art.

The invention claimed is: l

l. A light sensitive cell comprising the combination of a glass support with selenium and a conductive material comprising palladium on said support.

2. A light sensitive cell comprising a glass supporting member, selenium and a conductive metal support comprising a mixture of metals, one thereof being palladium adherent to said glass support, said selenium being in contact with said metal support.

3. A light sensitive cell comprising the combination of an insulating support, a conductive layer adherent thereto comprising a mixture of metals, one thereof being palladium, and selenium in contact therewith.

4. A light sensitive cell comprising a transparent support, a conductive support carried thereby and comprising a combination of metals including platinum and palladium, and selenium in contact with said conductive support.

5. A light sensitive cell comprising a glass support member, a conductive coating thereon comprising equal parts of platinum and palladium and a coating of crystalline selenium on said conductive coating.

6. A light sensitive cell comprising 4a glass support member, a conductive coating thereon comprising equal parts of platinum and palladium and a. coating of iodine treated selenium on said conductive coating.

ARTHUR W. CARPENTER. 

